Heterolepidoderma joermungandri, Kånneby, Tobias, 2011

Kånneby, Tobias, 2011, New species and new records of freshwater Chaetonotida (Gastrotricha) from Sweden, Zootaxa 3115, pp. 29-55 : 37-40

Heterolepidoderma joermungandri n. sp.

( Figures 6 , 7 )

Type locality. Sphagnum spp. rock pool, Skarvesäter, Bohuslän, Sweden (N 58º 14’ 23’’; E 11º 22’ 08’’).

Type material. Photographs of five specimens, available at the Swedish Museum of Natural History, Stockholm, Sweden. Accession numbers: Holotype, SMNH Type-8134; Paratypes, SMNH Type-8135 – SMNH Type- 8138.

Etymology. The species is named after the scaly Midgard serpent, believed to encircle the earth in Nordic mythology.

Diagnosis. Small species, 94–105 µm in total length. Body width 20–22 µm, 20–22 µm, 32–37 µm and 12 µm at head, neck, trunk and base of furca, respectively. Five-lobed head with cephalion and well developed hypopleuria. Anterior sensory bristles anchored by papillae, posterior sensory bristles anchored by double keeled scales. Straight furca, 13–15 µm in length, with rather thin adhesive tubes pointing slightly outward at distal end. Dorsal body surface covered by keeled scales distributed in 21–22 columns with 22–23 scales in each. Columns converging in the narrow parts of the body. Ventral interciliary area with keels and 1 to 2 pairs of larger keeled scales with simple spines. Ventral ciliation in two separate longitudinal bands. Mouth subterminal. Pharynx 27–29 µm in length, with anterior and posterior swellings and two cuticular reinforcements.

Description. Heterolepidoderma joermungandri n. sp. is a small-sized species, 94–105 µm in total body length. Head five-lobed, epipleuria barely visible while hypopleuria are well developed. Cephalion 12 µm in width. Two pairs of cephalic ciliary tufts, two cilia are considerably longer than the rest and reach lengths of up to 16 µm. Ocellar granules absent.

Body width 20–22 µm at the head (U8–9), 20–22 µm at the neck (U31–33), 32–37 µm at the trunk (U64–67) and 12 µm at the base of the furca (U88–90). Head slightly delimited from trunk by neck constriction that gradually widens into the trunk, which reaches its greatest width around U65–70. The trunk then tapers into a straight furca 13–15 µm in length with rather thin adhesive tubes, 7–8 µm in length, pointing slightly outward at their distal ends. Anterior and posterior sensory bristles present, anterior pair anchored by papillae at U24–25 and posterior pair anchored by double keeled scales at U82–86.

Dorsal body surface covered by 21–22 columns of 22–23 keeled scales with visible edges. The total number of columns is 34–38. The median column of dorsal scales is straight, except in the narrowest part of the neck region where it is replaced by two columns of diagonally arranged scales, while the columns on either side converge toward the narrower parts of the body. Just at the base of the furcal branches a pair of large rounded scales is present and just posterior to these on the inner edge of each furcal branch is an additional pair of keeled scales. The dorsal scales are hemi-elliptical in shape, 5–6 µm in length and 2–3 µm in width; with a prominent keel approximately 0.5 µm in height. The head and neck scales are more rhomboidal in shape, 4 µm in length and 2–3 µm in width. The interciliary area is covered by 7–10 columns of keels, scales apparently not developed, which can be followed past the pharyngeal intestinal junction. The posteriormost row (including terminal scales) consists of 2–4 larger keeled scales, approximately 5 µm in length, with a simple spine. Ventral ciliation in two separate longitudinal bands, not merging on the head.

Mouth subterminal, 4–5 µm in diameter; pharynx 27–29 µm in length with anterior and posterior swellings. Anterior region of pharynx reinforced by two cuticular rods just behind the mouth. Pharyngeal intestinal junction at U31–32. Intestine straight, anus situated at U87.

All observed specimens were adults in parthenogenetic phase.

Taxonomic remarks. Heterolepidoderma consists of 34 nominal species of which 20 are freshwater and 14 marine or brackish. Two species, H. fallax Remane, 1936 and H. loripes Martin, 1981 , are considered species inquirendae (Balsamo et al. 2009).

Heterolepidoderm a joermungandri n. sp. shows morphological characteristics found in both freshwater and marine species of the genus. Heterolepidoderma jureiense Kisielewski, 1991 and H. dimentmani Kisielewski, 1999 are freshwater species with cuticular reinforcements in the anterior part of the pharynx. The latter species can be separated from H. joermungandri n. sp. by its pronouncedly five-lobed head; moreover, the pharynx has two pairs of cuticular rods and an additional pair of cuticular granules compared to a single pair of cuticular rods and the absence of an additional pair of cuticular granules in H. joermungandri n. sp.

The pharynx in several marine species is reinforced with cuticular elements: Heterolepidoderma axi Mock, 1979 , H. clipeatum Schrom, 1972 , H. contectum Schrom, 1972 and H. foliatum Renaud-Mornant, 1967 all have hydrofoil scales which are absent in H. joermungandri n. sp. Marine species without hydrofoil scales but with cuticular reinforcements in the pharynx are H. armatum Schrom, 1966 , H. arenosum Kisielewski, 1988 , H. hermaphroditum Wilke, 1954 and H. istrianum Schrom, 1972 . H. armatum and H. istrianum are of a similar size but have fewer dorsal scale columns, 16–17 and 12–13 respectively vs. 21–22 and a different arrangement of head lobes compared to H. joermungandri n. sp. H. arenosum can be separated from the new species on the basis of possessing large ocellar granules and a longer furca and H. hermaphroditum on the basis of its clearly five-lobed head. H. caudosquamatum Grilli, Kristensen and Balsamo, 2009 , a brackish species described from Denmark, has hydrofoil scales and a lower total number of scale columns.

Of all the hitherto discussed species, H. joermungandri n. sp. seems morphologically most closely related to H. jureiense . Both species have similar body shapes and morphological and morphometric characters. However, H. jureiense has hydrofoil scales, which are absent in H. joermungandri n. sp., and has so far only been reported from Brazil.

Figures

FIGURE 6. Heterolepidoderma joermungandri n. sp. A) Habitus. B) Dorsal view of distribution and shape of scales. C) Habitus, arrow indicates cuticular reinforcement of pharynx and arrow heads indicate scales of the furcal base. Scale bars: A – C, 10 µm.

FIGURE 7. Schematic drawing of Heterolepidoderma joermungandri n. sp. Dorsal view to the left and ventral view to the right. Scale bar: 10 µm.